In a fuel cell system that supplies fuel gas containing hydrogen to a fuel electrode and supplies oxygen-containing gas to an oxygen electrode to perform power generation, an electrode reaction is blocked and thus power performance is decreased when a phenomenon, in which carbon monoxide (hereinafter, also called “CO”) adsorbs onto an electrode catalyst of the fuel electrode, so-called CO poisoning occurs.
As a process (hereinafter, also called “catalyst recovery process”) for resolving the CO poisoning, Japanese Patent Application Laid-Open No. 2005-25985 and Japanese Patent No. 5008319 disclose a method of causing fuel gas to be supplied to a fuel electrode to contain oxygen and thus oxidizing CO to detach it from an electrode catalyst. Moreover, Japanese Patent No. 3536645, Japanese Patent No. 4969955, and Japanese Patent No. 5151035 disclose related descriptions on the catalyst recovery process for the fuel electrode.